Development and Testing of Geopolymer Concrete
4.1 Introduction
4.2.3 Specimen preparation and curing
Chapter 4 Development and Testing of Geopolymer Concrete
and stirred properly. Later, the SP containing NaOH solution was added to the dry mix. In Type III, SP was added to the dry mix prior to the addition of NaOH solution. On addition of the SP, it was thoroughly mixed for homogenous distribution. NaOH solution was added to the mix at the end of this step of SP addition.
Controlled mix was prepared using PCC. Table 4.2 presents the mix proportion of PCC. The substrates for preparing slant shear test specimens were also cast using PCC. CC1 is the mix for substrate concrete. CC2 denotes controlled mix. The water/cement (w/c) and water/solid (w/s) ratios of PCC and GPC were same (except that of GC12 to GC17 and CC1).
Table 4.2: Mix proportion for PCC (kg/m3).
Mix Cement Fine Aggregate Coarse aggregate Water/cement (w/c)
CC1 360 680 1128 0.55
CC2 425 630 1190 0.40
Figure 4.1: Freshly prepared GPC.
For preparation of PCC, procedures mentioned in IS 516 1959 [122] were followed.
The curing of the specimens were conducted in similar way as that of the GPC specimens.
Compressive strength test was conducted on 150 mm cubes as per IS 516 1959 [122].
The freshly prepared concrete was placed into the cube moulds in three layers, each being compacted using an electric operated vibration table. The moulds were kept at ambient temperature of 20 ± 2 ºC. After 24 hours from the time of casting, the specimens were demolded and submerged inside water tank, maintaining temperature of 20 ± 2 ºC and stored till the arrival of test day. Fig. 4.2 shows the cubes being cured inside the water tank.
Figure 4.2: Concrete cubes under curing.
The size of cube specimens for pull-out test was also 150 mm. Provisions mentioned in IS 2770 1967 [123] were followed for the preparation of the specimens. Fig. 4.3 presents the special arrangements that were made for casting of the specimens for pull-out test. The
Chapter 4 Development and Testing of Geopolymer Concrete
special arrangement was provided to facilitate the vertical erection of the rebar that was supposed to be embedded partially inside the fresh concrete. A hole was also provided at the base plate of the cube to allow 5 mm length of the bar to remain outside the cube and also to facilitate the vertical erection of the rebar. Fig. 4.4 shows the details of the pull-out test specimen. The embedded length of rebar inside the cube was 50 mm. The remaining part of the rebar inside the cube was covered using poly vinyl chloride (PVC) tube to break the contact between the GPC and the surface of the rebar. PVC tube was used since it does not possess any reactive phenomenon with concrete. It is also water resistant, can withstand moderate temperature without deformation and is flexible. Before placing the concrete inside the pull-out test specimen, the rebar was placed inside the mould and allowed to stand vertical with the help of the special arrangement. The freshly prepared concrete was poured inside the mould in three layers taking care that the rebar did not dislocate from its position. For compaction of the concrete the moulds were vibrated after pouring of concrete in each layer.
The moulds were kept at ambient temperature of 20 ± 2 ºC. On completing of 24 hours from the time of casting, the specimens were demolded and submerged inside water tank, maintaining the temperature of 20 ± 2 ºC and stored till the arrival of test day. Fig. 4.5 shows the cubes being cured inside the water tank.
Figure 4.3: Mould for pull-out test specimens.
Figure 4.4: Details of specimens for pull-out test (All dimensions are in mm).
Figure 4.5: Pull-out test specimens under curing.
In the slant shear test specimens, the GPC constituted half of the volume. The other half, i.e. the substrate was prepared using PCC, mix CC1 (see Fig. 4.6). The PCC substrates were prepared with the help of dummy specimens which were cast, cured for 28 days and hand finished to give the perfect shape and slant angle of 30° along the surface ‘ab’ as shown in Fig. 4.6. The volume of each dummy specimen was half of that of cylindrical mould of size 75 mm diameter and 150 mm height [124]. Prior to the casting of the PCC substrate for slant shear test, the dummy specimens were placed into the cylindrical moulds with the surface ‘ab’ covered with polyvinyl sheet which acted as debonding media between the PCC substrates and dummy specimens. The fresh concrete for PCC substrate was prepared and
Chapter 4 Development and Testing of Geopolymer Concrete
placed into the moulds such that it occupied the other half of volume of the mould and kept for 24 hours at temperature of 20 ± 2 ºC. The size of the moulds were taken as 75 mm diameter and 150 mm height to economize the cost of the experimental study. Moreover, this study deals with the comparative behaviour of various mixes. Hence, the size effect on strength due to use of small moulds for slant shear test was not taken into account. The specimens were later demoulded and cured till 28 days from date of casting by submerging inside water tank, maintaining water temperature at 20 ± 2 ºC. After 28 days, the PCC substrates were cured in the open air till 2, 6 and 12 months from the date of casting, Fig. 4.7. At the end of open air curing period, the substrates’ surfaces ‘ab’ were carefully cleaned to peel off the dust layer, placed into the moulds and then the new GPC or PCC (CC2) was poured for each mix. The specimens were again kept into the mould for 24 hours at 20 ± 2 ºC. After 24 hours, these were demoulded and cured by submerging inside water tank maintaining temperature of 20 ± 2 ºC till the arrival of test day (Fig. 4.8).
(a) (b) (c)
Figure 4.6: (a) PCC substrate for slant shear specimen, (b) slant shear specimen, (c) details of specimens for slant shear test (All dimensions are in mm).
Figure 4.7: Curing of PCC substrates in water and open air.
Figure 4.8: Curing of slant shear specimens in water.